iommu/arm-smmu: Use a bitmap for the SMMU domain attributes

Use a bitmap to maintain the domain attributes for SMMU domains.
This simplifies the handling for the domain attributes, as it
removes the need to explicitly manipulate the bits, which can
be error-prone.

Change-Id: I719900df9d80801239b8e815d29953f3c6d067f0
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>